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RCD Protection at Data Cabinets

Bob Cowie
I have a Client that will not provide a Risk Assessment to omit an RCD Commando Socket for a Data Cabinet. He wishes to employ a local isolator for the Cabinet, however he is concerned that the PDU Strip that arrived on site from the factory and pre-fitted within the data cabinet would still need an RCD. It is my opinion that the Factory built Data Rack is classed as a piece of equipment and as such does not form part of the Contractor's installation. If the Rack had arrived on site without the PDU strip fitted and it was installed by the Contractor then this would form part of the installation and therefore would require an RCD. Any advice/assistance would be appreciated.
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    I've been thinking about this from a different direction, but I'm probably arriving at a similar conclusion to Graham (for once!).


    I've been thinking, not from a BS 7671 and equipment standards point of view, but from a Health & Safety at Work Act & Electricity at Work Regulations direction. The legislation doesn't distinguish between fixed wiring and other equipment, but concentrates on the overall level of safety. So say we had a rather uncontrolled environment. Rack placed alongside the system manager's desk in an open plan working area. IT guys aren't particularly knowledgable about mains electricity but know enough to get things to work. Not adverse to running a lead out from the rack to the desk if they need an extra socket for a new bit of equipment. Cleaner plugs their vacuum into whatever spare socket they can find. Likewise the mobile car valeting guy. Equipment from home sneaks in occasionally. Certainly not all IT offices are like that - but some are (I've been in them).  So we're now at a position where the "norm" is that ordinary sockets for general use are expected to have 30mA RCD protection - so what what your position be if someone used one of the non-RCD sockets supplied from the rack supply for something dodgy and came a cropper as a result?


    Hopefully at this point you're saying something like 'but my environment isn't like that - the rack will be in a locked machine room, or there's no chance of equipment outdoors being plugged into it, or the IT guys have been trained in some basic electrical safety - can't I take those factors into account' - to which I'd say yes of course - but the means the regs provide for doing that (paperwork wise) is via a risk assessment.


       - Andy.
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    Bob C:

    Gentlemen, I think we have drifted from my initial query. My question was about the internal power strip (generally 13amp) which arrives pre-fitted within the Data Rack. Is this classed as Equipment or is it part of the fixed wiring? The Client through his advisers consider it to be part of the fixed wiring and therefore should have RCD protection as they are unwilling to complete a risk assessment. Their initial thought was to fit an isolator above the rack negating the need for RCD protection and negating the need for them to produce a risk assessment, however they have now been advised that the power strip inside the cabinet requires an RCD or Risk assessment. Feedback from other bodies like Select advise that the power strip is not part of the fixed wiring and it does not come under the EICR therefore an RCD is not needed if you use an isolator rather than an external Commando socket, however if the Contractor fits the power strip after delivery of the rack it becomes part of the fixed wiring. I would appreciate comments on this point.




    To comply with BS EN 50310 fully, the power strip should have a supplementary bonding stud for connection to the rack earthing system for impedance control. This then effectively becomes part of the fixed wiring installation, because it has permanent equipotential bonding from the PE connection in the strip, to the rack earth bar. BS EN 50310 also contains a requirement to conduct impedance tests, so even if delivered "part assembled", still think there's some form of "fixed wiring tests".


    Even if the power strip is outside an EICR, BS 7671 can still be used to select and erect it, therefore I'm not 100 % convinced by that argument. I think this is the case even if the product comes fully or part assembled - it still contains 13 A socket-outlets, therefore the RCD issue of 411.3.3 should be addressed either by installation design (fitting the RCD in the fixed wiring installation), or by selection (i.e. rack has internal RCD protection to meet BS 7671 requirements).


    To comply with BS 7671, the 13 A socket-outlets in the rack require RCD protection, unless there is a risk assessment in place.


    The only other alternative to RCD or risk assessment is to use interconnection couplers (e.g. IEC 60320 J or F) on the power strips instead of BS 1363 socket-outlets. BS 7671 does not require cable couplers and interconnection couplers to be RCD protected, only socket-outlets.

     

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    Gentlemen, I think we have drifted from my initial query. My question was about the internal power strip (generally 13amp) which arrives pre-fitted within the Data Rack. Is this classed as Equipment or is it part of the fixed wiring? The Client through his advisers consider it to be part of the fixed wiring and therefore should have RCD protection as they are unwilling to complete a risk assessment. Their initial thought was to fit an isolator above the rack negating the need for RCD protection and negating the need for them to produce a risk assessment, however they have now been advised that the power strip inside the cabinet requires an RCD or Risk assessment. Feedback from other bodies like Select advise that the power strip is not part of the fixed wiring and it does not come under the EICR therefore an RCD is not needed if you use an isolator rather than an external Commando socket, however if the Contractor fits the power strip after delivery of the rack it becomes part of the fixed wiring. I would appreciate comments on this point.
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    davezawadi:


    There is a serious problem with the standards making process, and that is that interactions between various ones from differing sources lead to foolish and unnecessary outcomes. The most obvious one is electric cars (chargers) not being class 2 because someone didn't see that they could not safely be earthed in the external environment, which we all know and have a lot of regulations to reduce risks to presumably acceptable levels. However street furniture using PME is considered entirely satisfactory and does not cause a significant number of accidents. We need to be consistent on the basis of real risk only, not on "what if" scenarios.




    EV charging equipment and EVs are made for the global market, and are not limited to the UK. It seems that we in the UK are less happy with the problems that PME might bring ... However, is all this mis-placed? They are having a rough time with PME-related serious occurrences in Australia, not that I'm trying to draw direct parallels as Australia don't quite do things the way we do either.

    But let's be very clear that legislation is the driver here for considering PME risks in the UK, NOT standards.  It's the ESQCR (and its predecessors) that highlight the risk of PME in relevant circumstances, so that can't be ignored. There's not much difference between a caravan and an EV on charge, to be quite blunt; that is, if you ignore the fact that the caravan might have metal legs from the earthed chassis in contact with the ground, but an EV on charge won't !


    The other difference between general street furniture and EV charging equipment, in the main, is that of power rating. This is made quite plain in ENA ER G12/4.

     

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    I think that Andy has also made an error worrying about direct contact with damaged cables etc by anyone. Whilst that could happen given enough various circumstances, realistically it is very very unlikely. I would point out that a single RCD for a rack of servers (which might take 100A of mains, probably 3x32A supply) would be foolish, the idea of fitting one each is worse! We have an electrical system which depends on proper earthing of exposed conductive parts, and automatic disconnection of supply by CPDs, yet this regulation is determined to fit even more unnecessary RCDs! The scope for RCD protection is way too wide, it should only be for sockets where portable appliances are likely to be used by unskilled persons, and the servers in a rack should be out of scope for portable appliances separately, as you need tools to make them portable



    I agree RCDs aren't the solution - but I don't agree that the risk can be just ignored either. I've seen too many IT racks where things had obviously been put together in a very hap-hazard way, with everything from extra sockets provided by dangling supermarket 4-way extension leads, leads trapped in doors or slide rails, to mains leads with core insulation exposed. Pretty much all the horrors you see in some domestics. Also I don't think they're really in the usually-not-handled-when-live class of fixed appliances either - so much is hot swappable these days (usually PSU and fan modules are - some even allow hot addition of processors and memory) - and the idea of switching off before sliding a server out of the rack, or shoving an arm through the tangle of cables at the back to pull another lead through, just wouldn't be a consideration. If anything a restrictive conductive location might be a closer approximation. Like I said, I agree that 30mA RCDs aren't the answer, but I do see the risk assessment as a means of chivvying management into making sure their IT staff actually have a bit of basic electrical safety knowledge and implement some basic good practices.


      - Andy.
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    I think that Andy has also made an error worrying about direct contact with damaged cables etc by anyone. Whilst that could happen given enough various circumstances, realistically it is very very unlikely. I would point out that a single RCD for a rack of servers (which might take 100A of mains, probably 3x32A supply) would be foolish, the idea of fitting one each is worse! We have an electrical system which depends on proper earthing of exposed conductive parts, and automatic disconnection of supply by CPDs, yet this regulation is determined to fit even more unnecessary RCDs! The scope for RCD protection is way too wide, it should only be for sockets where portable appliances are likely to be used by unskilled persons, and the servers in a rack should be out of scope for portable appliances separately, as you need tools to make them portable.


    There is a serious problem with the standards making process, and that is that interactions between various ones from differing sources lead to foolish and unnecessary outcomes. The most obvious one is electric cars (chargers) not being class 2 because someone didn't see that they could not safely be earthed in the external environment, which we all know and have a lot of regulations to reduce risks to presumably acceptable levels. However street furniture using PME is considered entirely satisfactory and does not cause a significant number of accidents. We need to be consistent on the basis of real risk only, not on "what if" scenarios.
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    Beard Weird:



    This would have been an ideal topic to be forwarded to the IT section of the IET forum!


     




    It would certainly be an interesting discussion.


    edit: In fact, I've just posted a link to this Thread from the Data Centre Engineering Community discussions.

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    AJJewsbury:


     


    Same with plug and socket-outlet. They're all just isolators.



    Sorry, but I've got to disagree with that. Plugs & sockets mean that IT technicians and change the power supply arrangements safely. Bare in mind that when something goes wrong with live (i.e. customer facing) systems in the IT world there is huge pressure on technicians to get things working as quickly as possible - calling in an electrician who might not turn up for a few hours simply isn't an option. Being able to unplug a rack from one supply and plug it into another nearby supply has saved things on my watch at least once.


      - Andy.

     




    Well ... the original discussion point was that it was easy to get "mixed up" with an isolator, and that is what I was answering.


    I definitely get the point about quickly connecting to another supply, but of course that may mean making a decision whether it's safe to do so.


    It is still the case that making an assembly that doesn't really meet BS EN 61140 (in that the protective conductor current is too high, evidenced by the fact you can't use a 30 mA RCD) and then trying to treat it as a 32 A (or less) pluggable appliance, doesn't quite stack up. Basically, for pluggable equipment, the limit in BS EN 61140 for protective conductor current with rating > 20 A is 10 mA. To exceed this limit, the equipment should be permanently connected, AND have a reinforced protective conductor, AND be limited to a protective conductor current of 5 % of the phase current.


     

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    This does bring out a point from BS7671, which is the blanket requirement for RCDs for sockets up to 32A. In an installation such as this with supplementary bonding to earth, the RCD has exactly zero use!



    But supplementary bonding won't protect against instances of direct contact - e.g. from a damaged flex - where a 30mA RCD will provide some benefit. I've certainly seen flexes trapped in 19" rack doors and pulled around sharp edges of some of the metalwork before now. Certainly they're the situations it's easy to avoid with a bit of care - a policy of properly securing flexes and only allowing access to (authorized) persons with a bit of nous would seem to do - but we can't really assume that without a risk assessment to say that's the case. A lot of IT types, which very technical in some ways, really don't appreciate the hazards of mains electricity.


    Same with plug and socket-outlet. They're all just isolators.



    Sorry, but I've got to disagree with that. Plugs & sockets mean that IT technicians and change the power supply arrangements safely. Bare in mind that when something goes wrong with live (i.e. customer facing) systems in the IT world there is huge pressure on technicians to get things working as quickly as possible - calling in an electrician who might not turn up for a few hours simply isn't an option. Being able to unplug a rack from one supply and plug it into another nearby supply has saved things on my watch at least once.


      - Andy.
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    Well,  except for the potentially significant convenience of not having to turn the power off and verify exposed terminals are dead before unbolting things - as with signal cables, bonding can be removed and re-fitted, as soon as the jumbo mains plug is removed from the supply






    As long as you're not importing protective conductor currents from elsewhere.




    Yes you can have local isolation switches one per rack, but these in the heat of battle such things can be another source of accidentally switching off the wrong thing.






    Same with plug and socket-outlet. They're all just isolators. And many racks will have two feeds (or more) - multiple points of isolation. In terms of accidentally switching off the wrong thing in the heat of the moment, let's also consider Regulation 12 of the Electricity at Work Regulations 1989 which definitely requires "... where appropriate, methods of identifying circuits ...": if it's operationally so important not to "flip the wrong switches", make sure they are properly identified, because this is required for safety in any case.


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